Home › Words › L › legionellosislegionellosislegionellosis · noun — any disease caused by Legionella bacteria, such as Legionnaires' disease or Pontiac fever.Definition from Wiktionary (CC BY-SA 3.0).EtymologyFrom Legionella + -osis.nounAny disease caused by Legionella bacteria, such as Legionnaires' disease or Pontiac fever.Definitions & examples from Wiktionary (CC BY-SA 3.0).